Positive tri-position linear actuator

ABSTRACT

A tri-position linear actuator having a pair of pistons slideably mounted within an outer housing. These two pistons are actuated by a pressure differential. By varying the differential pressures acting on one or both of the pistons the actuator is moved to three distinct longitudinal positions.

mted States Patent 1 1 3,791,262 Staehlin et a]. Feb. 12, W74

[ POSITIVE TRI-POSITION LINEAR 1,918,426 7/1933 Radnor 92/52 x ACTUATOR 2,630,786 3/1953 Poore 92/52 X I 2,893,353 7/1959 Short, Jr. et al. 92/51 X [75] Inventors: John H. Stae in, Balumore; 3,179,019 4/1965 Cruse 92/51 William J. Meyer, Glen Burnie, both 3,696,712 10/1972 Sung 92/52 of Md.

[73] Assignee: The United States of America as FOREIGN PATENTS OR APPLICATIONS represented by the Secretary of the 937,859 9/ 1963 Great Britain 92/62 Air Force, Washington, DC.

[22] Filed: 1972 Primary Examiner-Edgar W. Geoghegan [21] Appl. No.: 215,444 Assistant Examiner-Abraham Hershkovitz Related US. Application Data [63] Continuation of Ser. No. 59,960, July 31, 1970,

abandoned. [5 7] ABSTRACT [52] US. Cl 92/52, 92/62, 92/65 A tri-position linear actuator having a pair of pistons [51] int. Cl. F01) 7/20 slideably mounted within an outer housing. These two Field of Search 63, pistons are actuated by a pressure differential. By 92/65 varying the differential pressures acting on one or both of the pistons the actuator is moved to three dis- R f r n Cited tinct longitudinal positions.

UNITED STATES PATENTS 2,554,614 5/1951 Carleton 92/65 X 2 Claims, 3 Drawing Figures I2 50 23 2a m 1 f so 22 1a POSITIVE TRI-POSITION LINEAR ACTUATOR This is a continuation of application Ser. No. 59,960, filed July 31, 1970, and now abandoned.

BACKGROUND OF THE INVENTION This invention relates generally to actuators and, more particularly, to a hydraulic or pneumatic actuator which is capable of movement to a plurality or distinct positions.

It is necessary in many instances to construct an actuator which is capable of movement to a plurality of distinct longitudinal positions. l-leretofore, such actuators were basically electrically operated and utilized a plurality of switches in order to move the actuator to the various distinct positions. These electrical switches were complex in nature and although fast-acting were highly unreliable due to power shortages or faulty electrical connections. Mechanical linkages were also available but these were either too slow-acting or easily jammed. There also have been numerous methods for causing an actuator to move from one discrete position to a second distinct position by fluid or-pneumatic means. The pneumatic actuators, although highly reliable and fast-acting, fell short in their usefulness since they were limited to either a fully retracted or fully extended position. In other words, heretofore there has been virtually no device which is capable of having a plurality of distinct positions and yet be of simple and reliable construction.

SUMMARY OF THE INVENTION This invention sets forth a unique hydraulic or pneumatic actuator which overcomes the problems set forth hereinabove.

The actuator of this invention is capable of movement to a plurality distinct positive positions, namely fully extended, fully reacted or partially extended. The actuator of this invention is basically made up of a piston within a piston operated within a cylinder. The innermost piston utilizes the inner diameter of the outer piston as its cylinder. Therefore, the position that the outer piston assumes controls the travel of the inner piston.

These three distinct positions are brought about by the positive action of a fluid or pneumatic source. This pneumatic source comprises a pressure port located at three distinct positions along the outer cylinder. In the fully reacted position of the actuator, two of the ports allow pressure to be admitted therethrough while one of the ports is vented to atmosphere. In the intermediate position, one of the ports is vented to atmosphere, while out of the remaining two ports which admit pressure therethrough, one of the ports admits a greater pressure than the other. In the third or fully extended portion only one of the ports admits pressure therethrough, while the two remaining ports are vented to the atmosphere. Such a tri-position actuator, as set forth in this invention, is easily manufactured, has relatively few moving parts; is a quick operating and highly reliable device.

It is an object of this invention to provide a positive tri-position linear actuator which moves to three distinct positions by the utilization of a fluid or pneumatic source.

It is another object of this invention to provide a positive tri-position linear actuator which is fast-acting, highly reliable and has a minimum of moving parts.

It is still another object of this invention to provide a positive tri-position linear actuator which is economical to produce and which utilizes conventional currently available components that lend themselves to standard mass producing manufacturing techniques.

For a better understanding of the present invention together with other and further objects thereof, reference is made to the following description taken in connection with the accompanyingdrawing and its scope will be pointed out in the appended claims.

DESCRIPTION OF THE DRAWING FIG. 1 is a side elevational view of the actuator of this invention, shown partly in cross-section and in its fully retracted position;

FIG. 2 is a side elevational view of the actuator of this invention shown partly in cross-section and in its intermediate position; and

FIG. 3 is a side elevational view of the actuator of this invention shown partly in cross-section in its fully extended position.

DESCRIPTION OF THE PREFERRED EMBODIMENT Reference is now made to FIG. 1 of the drawing which discloses the hydraulic or pneumatic actuator'10 of this invention in its fully retracted position. The actuator 10 is made up of an innermost piston 12 located within an outer piston 14 and an outer cylindrical housing 16. The pistons 12 and 14 and cylinder 16 may be made of any suitable material, such as metal or hard plastic. It should be noted, however, that although only a pair of pistons 12 and 14 are shown in the drawing the actuator 10 of this invention can be formed with as many of these pistons as space will allow in order to expand the number ofdiscrete positions the actuator 10 may move to.

The inner piston 12 has formed at one end thereof an elongated member 18 which is utilized as the actuating element of this invention and formed at substantially near the other end of piston 12 is an outstanding element 20 acting as a stop means. An indented portion or groove 22 is also formed at this end of inner piston 12 acting as a fluid reservoir and utilized during the operation of actuation 10 in a manner to be explained in detail hereinbelow.

Surrounding inner piston 12 is an outer piston 14 made up of an outstanding stop element 24 at one end thereof and having a pair of apertures 26 and 28. One of these apertures 28 is located adjacent the outstanding element 24, while the other aperture 26 is located at the other end of piston 14 adjacent reservoir 22 of piston 12. These apertures 26 and 28 allow for the passage of fluid therethrough in order for the pressurized fluid to move the outer piston 14 and the inner piston 12 to their desired positions.

Surrounding the inner piston 12 and the outer piston 14 is a cylindrical housing 16 having a pair of closed ends 30 and 32 which act as both stop means and fluid sealing means. In the actuator 10 of this invention there are three apertures 34, 36 and 38 located within the cylindrical housing 16. These apertures 34, 36 and 38 are so positioned along the cylindrical housing 16 that aperture 34 is aligned with aperture 26 of outer piston 14 in the positions shown in FIGS. 1 and 2 and aperture 36 is aligned with aperture 28 of the outer piston 14 in the same positions. Aperture 38 of outer cylinder 16 is formed adjacent the end wall 32 and allows for the passage of fluid into chamber 40 between inner piston 12, outer piston 14 and outer cylinder 16. A plurality of conduits 42, 44 and 46 are attached to apertures 34, 36 and 38, respectively, in order to permit the passage of "fluid therethrough from any conventional pressure source 48.

Referring to FIG. 2, the actuator is shown in its partially extended or second position in which aperture 34 remains aligned with aperture 26 on outer piston 14 and wherein fluid such as air, under a known pressure, is admitted therethrough in order to move the inner piston 12 to the partially extended position shown in FIG. 2. Simultaneously, a fluid under greater pressure than the pressure through aperture 34 is admitted through aperture 38 in order to prevent the movement of outer piston 14 during this operation. Aperture 36 on outer cylinder 16 which is aligned with aperture 28 of outer piston 14 is being vented to the atmosphere. In the position shown in FIG. 2, the outstanding element 20 of piston 12 abuts the outstanding element 24 of piston 14 to limit the motion of inner piston 12. It should again be noted that in order to prevent the movement of the outer piston 14, it is necessary for the pressure passing through aperture 38 of outer cylinder 16 to be greater than the pressure passing through aperture 34.

Referring now to FIG. 3 in which the actuator 10 of this invention is in the fully extended or third position, the fluid under pressure is admitted through aperture 34 alone, while apertures 36 and 38 are vented to the atmosphere. This admission of pressure through aperture 34 allows for the movement of outer piston 14 to the position shown in FIG. 3 with its outstanding element 28 finally coming to rest against the outer end 32 of cylindrical housing 16. The inner and outer pistons 12 and 14 are held in axial alignment against one another and against outer cylindrical housing during the entire operation of actuator 10 by means of guides 50. These guides 50 allow for the slideable motion of the pistons 12 and 14 against one another and against outer cylindrical housing 16 with a minimum of friction and may be lined on the bottom thereof with any suitable low friction substance, such as Teflon.

It should be noted, that although the actuator 10 of this invention is shown in three distinct positions of movement, the actuator 10 may be modified so that a plurality of other positions can be brought about with the addition of the appropriate number of pistons, stops, apertures, and pressure sources.

MODE OF OPERATION Reference is once again made to FIG. 1, wherein the actuator 10 of this invention is shown in its fully retracted position. In this position the inner piston 12 and the outer piston 14 rest against one end 30 of cylindrical housing 16 of actuator 10 with the application of fluid under pressure through both apertures 36 and 38 in order to prevent the movement of pistons 12 and 14. By venting aperture 36 to atmosphere and applying fluid under pressure to apertures 34 and 38 (with the pressure through aperture 38 being greater than through aperture 34), the inner piston 12 moves to its partially extended position as shown in FIG. 2. The fluid under pressure through aperture 34 moves the inner piston 12 against the outstanding member 24 on outer piston 14 while the even greater pressure of the fluid through aperture 38 prevents the movement of the outer cylinder 14. By now applying fluid under pressure only through aperture 34 and venting apertures 36 and 38 to the atmosphere, both the outer piston 14 and inner piston 12 move under this pressure to the fully extended position as shown in FIG. 3, wherein outstanding element 24 abuts the end 32 of the cylindrical housing 16.

In order to retract the actuator 10 of this invention, the pressure is initially applied to aperture 38, while aperture 34 and 36 are vented to atmosphere in order that the outer piston 14 moves to the position shown in FIG. 2. In order to move the inner piston 12 to the fully retracted position, the pressure is now applied to apertures 36 and 38, while aperture 34 is vented to the atmosphere as shown in FIG. 1.

It is this application of fluid under pressure and the venting to the atmosphere within the cylindrical housing 16 which allows for the movement of the elongated actuating element 18 of actuator 10 of this invention to the plurality of distinct longitudinal positions. Any suitable combination of fluid under pressure may be utilized in order to move the actuator 10 to its desired positions.

Although the invention has been described with reference to a particular embodiment, it will be understood to those skilled in the art that the invention is also capable of a variety of alternate embodiments such as an actuator with additional pistons and apertures within the spirit and scope of the appended claims.

We claim:

1. A pneumatic actuator comprising an outer housing having a first, second and third aperture therein, a first piston slideably mounted within said outer housing, said first piston being completely open at one end thereof, having an outstanding element at an end opposite said one end thereof and having a first and second aperture therein, a second piston slideably mounted within said first piston, a reservoir formed at one end of said second piston between said second piston and one end of said housing for receiving fluid, a first chamber formed adjacent said first piston and said second piston for receiving fluid, a second chamber formed at an end opposite said one end of said housing directly adjacent said outstanding element of said first piston between said outer housing, said first piston and said second piston for receiving fluid, said first aperture in said first piston connecting said first housing aperture to said reservoir, said second aperture in said first piston connecting said second housing aperture to said first chamber, said third housing aperture being connected to said second chamber and a pressurized fluid source being connected to said housing apertures whereby the application or removal of a fluid pressure through said housing apertures causes the movement of said pistons to a plurality of distinct positions.

2. A pneumatic actuator as defined in claim 1 wherein said second piston has an elongated element at an end opposite said one end thereof, said elongated element extending beyond said outer housing. 

1. A pneumatic actuator comprising an outer housing having a first, second and third aperture therein, a first piston slideably mounted within said outer housing, said first piston being completely open at one end thereof, having an outstanding element at an end opposite said one end thereof and having a first and second aperture therein, a second piston slideably mounted within said first piston, a reservoir formed at one end of said second piston between said second piston and one end of said housing for receiving fluid, a first chamber formed adjacent said first piston and said second piston for receiving fluid, a second chamber formed at an end opposite said one end of said housing directly adjacent said outstanding element of said first piston between said outer housing, said first piston and said second piston for receiving fluid, said first aperture in said first piston connecting said first housing aperture to said reservoir, said second aperture in said first piston connecting said second housing aperture to said first chamber, said third housing aperture being connected to said second chamber and a pressurized fluid source being connected to said housing apertures whereby the application or removal of a fluid pressure through said housing apertures causes the movement of said pistons to a plurality of distinct positions.
 2. A pneumatic actuator as defined in claim 1 wherein said second piston has an elongated element at an end opposite said one end thereof, said elongated element extending beyond said outer housing. 